Process for the production of cellulose esters



Patented Nov. 10, 1931 PATENT o FrcE.

HENRYDREYFUS, OF LONDON; ENGLAND" v PROGESS'FOR; PRODUCTION OF QELLULOSEESTERS No Drawing. Application filed:November 30, 1925, Seria1No.':72,403, and in GreatBritainiOetober30;19255:-

This invention relates to the production. of

cellulose acetate or-other cellulose esters In my French specificationNo. 565,654,

and my U. S. application SerialNo. 633,016,

I have described inter aliahow'cellulosic materials may bepretreatedwith. organic, acids, such as acetlc acid or formic acld and the like,at ordinary or raised temperatures or with cooling before subjecting;thenrto acetylation or other esterification, while in U. S. applicationSerial No. 7 47 ,054 and'British application No. 22697/24 I havedescribed how such pretreatment with organic. acids may be preceded,particularly in the case-10f cellulosic materialsother thancotton such.

as wood pulps, by a. treatment with alkaline substances to. render .thematerials more re-. active to acetlylation-u or other esterification.

Further in U. S. application Serial :No.

J 66,103 and British application No. 24,867/25, I have described how.thepretreatment may be carried out with :vapors of the. organic.

acids, particularly lower fatty acidsssuch as formic or acetic acid,the'vaporsbeing em-. ployed alone or in admixtureiwith ,air or otherinert-gas, orbeing generatedby soaks, ing the materials in theconcentrated or dilute 1 acids and subsequently passing air or; otherinert gas through the materials. Preferably after the treatment airorother inert gasis passed through the materials to remove the organicacid wholly or partially,

Hitherto it has not been possible to obtain 1 usefulcellulose esters orcellulo-sewacetateby esterifying or acetylating cellulose- 1n: ab-.

sence or substantially in absence of benzol lulose ester is producedsubstantially in the solid or fibrous state and not in form of itssolution). This was due to many reasons,

such as, amongst others, the quantities. of.

condensing agent (suchas sulphuric acid) employed, which gave rise toso-muchheati acetylizing or other esterifyingsolution is 1 necessary.Further, the acetylationor other esterification: products produced aremuch morehomogenous and cleaner anclpresentmany other advantages. whichwill be evident and require no mention here. v r

According to the present invention l produce cellulose acetates or othercellulose es ters by subjecting cellulosic materials. which havepreviously been subjected to pretreat- ,ment with organic acids inthemannerlin dicated in my previous patents and'applicationsrefe-rre-dto above, to acetylation or-esg' terification in suspension inabsence orsub.- stantially in absence of benzol or 0ther.1iq-; uiddiluents. (That is, thecellulosic material is subjected to acetylat-ionor ester-ification in their natural or fibrousvstate. inabsence orsubstantially in absence of benzol H or other liquid diluents'and inabsence of, liquid solvents or in presenceof suchsmallr V quantities ofliquid solvents that the cellulose: acetates or other cellulose estersare produced. substantially in the solid or; fibrous state and notinform of their solution). The acetylation or other esterification iseifecteclby pass I ingthe vapours of the acetylating or otheresterifyingagent or agents, overv or through the said cellulosic materials p Thereaction is preferably performedin presence of condensing agents,andi'particularly sulphuric acid, by first impre'gnatingv the cellulosicmaterials inw any suitable manner. with the condensing: agent or agents.Other methods of applyingthe condensing agents may however be (em-sployed as hereinafter; explained, on the reaction may be carried outwithout condensing agents. Further the vapors of the acetylating orother esterifying agent or agents may be mixed with vapors of solvents,such as acetic acid vapor, and with air or other indifferent gas orgases.

In performing the invention, I may first impregnate the aforesaidpreheated cellulosic materials with a relatively small or reducedquantity of condensing agent, such as sulphuric acid, for example aboutto 3% on the weight of the cellulosic materials, for instance byimpregnating with a solution of the condensing agent in water or aceticacid and then removing partially or entirely the acetic acid or water bypressing out, hydroextracting, or drying, or by passing a stream of airor other indifierent gas or gases through the material, or even moisturein the form of acetic acid or some water may be left in the material.

It is of course understood that pretreatment with organic acids such asacetic acid in the liquid state may, if desired, be combined with theimpregnation with the condensing agent and be performed for example in'the manner indicated in my previous French Patent 565654 or my U. S.application S. 633,016, after whichand prior to acetylation or otherest-erification-the acetic or other organic acid is removed partially orentirely 1n the manner above ind1cated, i. e.

by pressing out, hydro-extr acti ng, by drying or by passing air orother indlfierent gas or gases through the material.

Instead of employing relatively small or reduced quantities ofcondensing agent or agents, I may employ larger quantities, but theemployment of larger quantities is not attended with any advantages.

After impregnation the cellulosic material may be submitted toacetylation or other esterification by passing over or through saidmaterial the vapours of the acetylating or other esterifying agent oragents in presence or absence of vapours of organic acids, such asacetic acid, and preferably in aomixture with air or like indifferentgas or gases. Thus, for example, I may employ a mixture of air or otherindifferent gas or gases and acetic anhydride vapour, or a mixture of iror other indifferent gas orgases and the vapours of acetic anhydride andacetic acid. Suchmixtures may be formed in any suitable way as, forinstance, by simply mixing the gases and vapour, but preferably they areformed by passing air or other indifferent gas or gases through aceticanhydride or acetic anhydride mixed with acetic acid in the cold or withheating. The cellulosic materials are preferably subjected to constantmoving or agitation mechanically during the acetylation or otheresterification, as for instance by subjecting them to the action'of thesaid vapours or mixtures of said vapours and air or the like inrevolving drums or the like. Less preferably the reaction may beperformed without this agitation or moving.

The reaction may if desired be performed with heating, the cellulosicmaterials and/or the said vapours (or mixtures containing the same)being heated; the reaction may, however, be also performed withoutheating, though without heat the reaction may take longer to perform.

Further, if condensing agents of a volatile nature are employed, theymay be passed together with the vapours of the acetylating or otheresterifying agent (or mixtures of said vapours with air or otherindifferent gas or gases) over or through the cellulosic material,whether or not said cellulosic ma terial has previously been impregnatedwith catalysts. Even sulphuric acid may be .e'm-

ployed'in this manner, as it is to a certain extent volatile. Froma'practical point of view, however, there is no advantage in employingsulphuric acid in this manner as the reaction is too slow.

If desired thevapours of theacetylating or other esterifying agent oragents may be passed over or through the cellulosic materials withoutbeing admixed with air or othermdifi erent gas or gases, for mstance bypass-- vapours are adjusted co-compensate changes in their constitutionincurred in the reaction. Thus, for example, when acetic anhydride aloneor in admixture with air or other indifferent gas or gases and mixed ornot with acetic acid vapour, is passed over or through the cellulosicmaterials, the issuing vapours will contain a'certain amount of aceticanhydride, but before passing the vapours again over or through thecellulose materials it is preferable to add more acetic anhydride to thevapours to compensate for the acetic anhydride used upvin the reaction;however, the vapours may be passed without further additions until theanhydride is substantially exhausted. 1

The reaction may be continued until the desired degree of acetylation oresterification has been reached, which may be found for example byanalysis of the products or tests as to their solubility in the desiredsol- .vent or solvents.

(mercerized or non-mercerized), wood pulps (for instance wood pulp whichhas been pre-' viously submitted to a treatmentwith alkali, or alkalinesubstances such as barium hydroxide, sodium Zincate, sodium aluminate,or organic bases especially the alkaline treatment indicated in myprevious British appli-' cation No. 22697 /1924 and U. S. application S.747,054) or other cellulosic materials or conversion products which havebeen submitted to the hereinbefore indicated pretreatments whether ornot such pretreated materials have been deprived, prior to theacetylation, substantially or entirely of acetic acidwhere acetic acidis used for the said pretreatments. Thus, where acetic acid is usedeither in vapour form or in the liquid state for the hereinbeforeindicated pretreat- 1-. ments, the cellulosic materials may beoptionally deprived (partially or entirely) of the acetic acid prior toacetylation or other esterification, for example by subjecting them to astream of air or other indifferent gas or gases, or when liquid aceticacid is used, by hydro-extraction, pressing out or the like, with orwithout subsequent subjection to a stream of air or other indifferentgas or gases. When formic acid is used for the hereinbefore indicatedpretreatment-s the cellulosic materials are preferably deprived (forexample in a manner analogous to that indicated for acetic acid above)of the formic acid prior to acetylation or other esteritication, toavoid reactions with the acetic anhydride or other esterifying agent oragents.

The cellulose acetates or other cellulose esters produced by the processof the present invention may, if desired, be subjected to secondarytreatments or reactions for the purpose of changing their solubilities,either before or after stabilization and/or elimination orneutralization of the condensing agents. Such secondary treatments orreactions may be performed in suspension or after firstdissolving thecellulose acetate or other esters in acetic acid or other solvents.Preferably, however, I perform the secondary treatment by subjecting thecellulose derivatives, after the acetylation or other esterification, tothe action of vapours of formic or acetic acid (or mixtures thereof)containing sufiicient humidity to destroy any anhydride or otheresterifying agent remaining in the cellulose derivatives or evencontaining excess of humidity or water vapour. Or less advantageously Imay employ water vapour or humidity alone, employing, for example,reduced quantities of water vapour in. ad-

mixture with air orlike indifferent gas or gases. The vapours may bepassed over orthrough the materials in a manner analogous to thatemployed in the acetylation or esterification process, i. e. they may beemployed in admixture or not with air or other indifferent gas or gasesand passed over or through thecellulose derivatives, preferably whilesubjecting i the latter to moving or agitation, for example in revolvingdrums or the like. Further, va-

pours ofhydrochloric acid, nitric acid vapours, or other vapours may, ifdesired, be employed in admixture with the organic acid vapours or watervapours. Thus for example I may employ vapours of acetic acid or formicacid (or mixtures thereof) loaded I with some hydrochloric acidvapour ornitric acid orother vapour, in presence or absence of more or lesshumidity promoting solubility changes. tures in the cold and by passingthem in admixture with air or otherindiiferent gas or gases when mineralacids vapours are used, but when employing organic acids such as aceticacid I may heat up to temperatures such as to 100 C., so as toaccelerate the reaction. I i

The above special form of execution of the secondary treatments orreaction is of course given only by way of illustration and is in no waylimitative.

Further, I may perform the secondary treatments or reactions after firstdissolving up the cellulose derivatives in acetic acid or othersolvents, or after first forming suspensions of the cellulosederivatives, for example by adding benzol or like diluents in presenceor absence of acetic acid or the like. In such cases the secondarytreatments or reactions maybe performed for example by the methodsdescribed in my prior British Patents Nos. 20,852/1912, 207,562, my U.S. reissue Patent 14,388 and my U. S. application S. 633,016, and myBritish Patent 20,977/ 1911 and U. S. Patent 1,217 ,722, the two latterof which in particular describe in detail processes of further treatmentfor transforming. primary acetylation products into products havingother solubilities as desired, and to which I refer for the sake ofbrevity. In these specifications above referred to I have shown 'how theprimary esterification products or their esterification solutions orotherwise m'ade iup solutions of them, or in suspension, can be thustransformed by using, the direct a'cetylation solutions or other solu-'tions of the primary esterification products, with or without theaddition of water or other similarly acting agents having the effect ofdestroying acetic anhydride and which at the same time should preferablybe able to be themselves esterified without producing water in any wayeven intermediately, as for instance lactic. acid (the absenceof wateror similarly acting agents in the treatment or the quantity of water orsimilarly acting ties passed through).

I have also there described how the esteriiication solutions can betreated by neutralizing the efiect of the condensing agent partially orcompletely and be submitted in such form to a secondary treatment eitherat ordinary temperature or with heating to a higher temperature foraccelerating the reaction, that is to say, by having really only freeorganic acids as explained for example in my U. S. Patent 1,217,722 page4, lines 119, 120-129.

Furthermore, I have shown in my said patents that the weaker thecondensing agent the more water or similarly acting agents one can usein the secondary reaction for getting given phases of solubilities, notexcluding, however, the use of less water or similarly acting agents orno water or similarly acting agents for passing through many more phasesof solubilities more slowly and therefore more distinctly, whilst if thecondensing agents are stronger the quantities of water or similarlyacting agents have to be reduced in order to get certain solubilitiesbased on a given acetylation solution, unless certain or given phasesolubilities are to be passed over or never appear.

For the sake of brevity, only these facts are mentioned as having asimilar bearing or application here, but for details reference may behad to the above mentioned patents where these matters are fullyexplained.

By way of example, the further treatment to vary the solubilities of theprimary esterilication products may be effected by exposing them to thefurther treatment after firstdissolving them in acetic acid or likesolvents or after first forming suspensions of them in benzol or likediluents in presence or absence of acetic acid or the like, it beingremembered that in conducting the secondary reaction any excess orremaining anhydride has first to be destroyed by water or otheranhydride-destroying agents which should preferably be themselvescapable of esterification without producing water, e. g. lactic acid,and that the secondary reaction may proceed in the absence or in thepresence of Water or similarly acting agents, and that according to the.

quantity of water or similarly acting agents used or present in thesecondary reaction, and to the time of reaction and temperatureobserved, different phases of solubilities can be reached and disappearagain according as the reaction is prolonged, it being understood thatthe less the amount of water or similarly acting agent used the greaterwill be the range of these phases. I 1

T he further treatment or reaction may preferably take place at aboutordinary temperature, or as explained in my said patents,

a ents used directing the phasesof solubilithe present invention do notnecessarily correspond to those developed in the products obtainedaccording to my said previous British Patents 20977/1911, 14101/1915,6463/ 1915, 100009 and 207562 and U. S. patents Reissue 14,338,1,278,885,1,280,974,1,280,975 and U. S. application S. 633,016, inasmuchas the primary acetylation products obtainable by the new process of thepresent invention may have other solubilities than those producedaccording to mysaid previous patents.

What I claim and desire to secure by Letters Patent is I 1. Process forthe production of cellulose esters comprising pretreating cellulosicmaterials with an agent containing vapors of lower fatty acids as soleactive agents and thereafter esterifying said pretreated materialssubstantially in absence of liquid solvents and diluents by subjectingthem to the action of vapors of the csterifying agent.

2. Process for the production of cellulose .cecates comprisingpretreating cellulosic a tic acid as sole active agent and thereafterstantially in absence of liquid solvents and.

diluents by subjecting them to the action of vapors of the acetylatingagent.

8. Process for the production of cellulose acetates comprisingpretreating cellulosic materials-with an agent containing vapors offormic acid as sole active agent and thereafter acetylating saidpretreated materials substantially in absence of liquid solvents anddiluents by subjecting them to the action of vapors of the acetlylatingagent.

41. Process for the production of cellulose esters comprisingpretreating cellulosic materia swith an agent containing vapors of lowerfatty acids as sole active agents and "hereafter esterifylng saidpretreated materials substantially in absence of liquid solvents anddiluents by subjecting them in presence of a condensing agent to theaction of vapors of the esterifying agent.

i 'rocess for the production of cellulose esters comprising pietreatingceilulosie materials with anagent containing vapors of lower fatty acidsas sole active agents and thereafter esterifying said pretreatedmaterials substantially in absence of liquid solvents and diluents'bysubjecting them in presence of a condensing agent to the action of amixture of vapors of the esterifying agent and an indifferent gas.

naterials with an agent containing vapors of,

ce acetvlating said pretreated materials sub- 6. Process for theproduction of cellulose esters comprising pretreating cellulosicmaterials with an agent containing vapors of formic acid as sole activeagent and thereafter esterifying said pretreated materials substantiallyin absence of liquid solvents and diluents by subjecting them inpresence of a condensing agent to the action of a mixture of vapors ofthe esterifying agent and an indillerent gas.

7. Process for the production of cellulose esters comprising pretreatingcellulosic materials with an agent containing vapors of aceticacid assole active agent and thereafter esterifying said pretreated materialssubstantially in absence of liquid solvents and diluents by subjectingthem in presence of a condensing agent to the action of a mixture ofvapors of the esterifying agent andan indifferent gas.

8. Process for the production of cellulose esters comprising pretreatingcellulosic materials with an agent containing vapors of acetic acid assole active agent and thereafter esterifying said pretreated materialssubstantially in absence of liquid solvents and diluents by subjectingthem in presence of a condensing agent to the action of a mixture ofvapors of acetic anhydride and an indifferent gas. a

In testimony whereof I have hereunto subscribed my name.

HENRY DREYFUS.

